Enzyme Replacement Therapy (ERT) A therapy designed to address the underlying enzyme deficiency associated with a lysosomal storage disorder or other disease characterized by an enzyme deficiency.

Host Cell A cell that has been genetically modified to produce a specific protein and is used as a ‘seed’ to produce cells which are identical to it (a cell line).

Lysosomal Storage Disorder (LSD) A disorder characterized by the buildup of substrates within the lysosomes of cells.

Lysosome A cell organelle that digests wastes and materials within the cell using enzymes.

Mucopolysaccharidosis I (MPS I) A lysosomal storage disorder characterized by a deficiency of the enzyme, alpha-L-iduronidase.

Mucopolysaccharidosis VI (MPS VI) A lysosomal storage disorder characterized by a deficiency of the enzyme, of N-acetylgalactosamine 4-sulfatase (arylsulfatase B).

Organelle A small structure within a cell that performs a dedicated function, analogous to an organ in the human body.

Orphan Drug Designation A U.S. Food and Drug Administration designation conferred upon investigational products that are being developed for diseases that affect fewer than 200,000 patients in the United States. Products with orphan drug status that are the first to be approved for a specific indication have seven years of market exclusivity within the United States.

Orphan Medicinal Product Designation A European Medical Evaluation Agency designation conferred upon investigational products for diseases that affect fewer than five in 10,000 patients in the European Union. Products with orphan medicinal status that are the first to be approved for a specific indication have 10 years market exclusivity within the European Union.

Phenylalanine Hydroxylase (PAH) An enzyme needed to metabolize phenylalanine, an amino acid found in most protein-containing foods. People with the disease PKU lack sufficient quantities of this enzyme.